U.S. patent number 6,575,566 [Application Number 10/246,491] was granted by the patent office on 2003-06-10 for continuous inkjet printhead with selectable printing volumes of ink.
This patent grant is currently assigned to Eastman Kodak Company. Invention is credited to Gilbert A. Hawkins, David L. Jeanmaire, Ravi Sharma.
United States Patent |
6,575,566 |
Jeanmaire , et al. |
June 10, 2003 |
Continuous inkjet printhead with selectable printing volumes of
ink
Abstract
An inkjet printhead, that includes a plurality of nozzle bores
from which streams of ink droplets having selectable first and
second volumes are emitted; a droplet deflector for deflecting the
ink droplets having first and second volumes into first and second
paths respectively, the droplet deflector producing a corresponding
plurality of physically separate streams of gas, each stream of gas
directed on a corresponding one of the streams of ink droplets; and
an ink gutter positioned to catch the ink droplets moving along one
of the first or second paths. In addition to a method for
selectively controlling the ink droplets with the aforementioned
inkjet printhead.
Inventors: |
Jeanmaire; David L. (Brockport,
NY), Hawkins; Gilbert A. (Mendon, NY), Sharma; Ravi
(Fairport, NY) |
Assignee: |
Eastman Kodak Company
(Rochester, NY)
|
Family
ID: |
22930898 |
Appl.
No.: |
10/246,491 |
Filed: |
September 18, 2002 |
Current U.S.
Class: |
347/77;
347/82 |
Current CPC
Class: |
B41J
2/03 (20130101); B41J 2/09 (20130101); B41J
2/105 (20130101); B41J 2002/022 (20130101); B41J
2002/031 (20130101); B41J 2002/033 (20130101) |
Current International
Class: |
B41J
2/07 (20060101); B41J 2/03 (20060101); B41J
2/015 (20060101); B41J 2/09 (20060101); B41J
2/105 (20060101); B41J 2/075 (20060101); B41J
002/02 (); B41J 002/09 (); B41J 002/105 () |
Field of
Search: |
;347/74,75,77,82 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Vo; Anh T. N.
Attorney, Agent or Firm: Shaw; Stephen H.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
Reference is made to commonly assigned, co-pending U.S. patent
application Ser. No. 09/751,232, filed Dec. 28, 2000, titled "A
Continuous Ink-Jet Printing Method And Apparatus," by D. L.
Jeanmaire, et al., U.S. patent application Ser. No. 09/750,946,
filed Dec. 28, 2000, titled "Printhead Having Gas Flow Ink Droplet
Separation And Method Of Diverging Ink Droplets," by D. L.
Jeanmaire, et al., and U.S. patent applications Ser. No.
10/100,376, filed Mar. 18, 2002, titled "A Continuous Ink Jet
Printing Apparatus With Improved Drop Placement," by D. L.
Jeanmaire.
Claims
What is claimed is:
1. An inkjet printhead, comprising: a) a plurality of nozzle bores
from which streams of ink droplets having selectable first and
second volumes are emitted; b) a droplet deflector for deflecting
the ink droplets having first and second volumes into first and
second paths respectively, the droplet deflector producing a
corresponding plurality of physically separate streams of gas, each
stream of gas directed on a corresponding one of the streams of ink
droplets; and c) an ink gutter positioned to catch the ink droplets
moving along one of the first or second paths.
2. The inkjet printhead as claimed in claim 1, wherein the streams
of gas are provided by individual jets as defined by a plurality of
slits in a plate structure such that a gas flow discriminator is
formed.
3. The inkjet printhead as claimed in claim 1, wherein the streams
of gas are positive from a pressure source above ambient.
4. The inkjet printhead as claimed in claim 1, wherein the streams
of gas are negative from a pressure source below ambient.
5. The inkjet printhead as claimed in claim 1, wherein actuators
are provided in said droplet deflector, such that the streams of
gas are independently adjustable for each of the streams of ink
droplets.
6. The inkjet printhead as claimed in claim 1, wherein the streams
of gas are applied in a direction substantially perpendicular to
one of the first or second paths of ink droplets.
7. The inkjet printhead as claimed in claim 1, wherein one of the
first or second paths of ink droplets includes a gutter path.
8. The inkjet printhead as claimed in claim 1, wherein one of the
first or second paths of ink droplets includes a printing path.
9. The inkjet printhead as claimed in claim 2, wherein the plate
structure includes slits spaced equivalent to the plurality of
nozzle bores.
10. The inkjet printhead as claimed in claim 2, wherein the plate
structure includes a plenum that draws one of the first and second
volumes of streams of ink droplets into the plenum.
11. The inkjet printhead as claimed in claim 5, wherein the
actuators respond to resistive heating from the passage of an
electrical current.
12. An inkjet printhead, comprising: a) one or more nozzle bores
from which a stream of ink droplets of adjustable volumes are
emitted; b) at least one heater associated with each of the nozzle
bores and adapted to independently adjust the volume of the emitted
ink droplets, wherein the emitted ink droplets, categorically, are
within a first or a second range of unequal volumes c) a droplet
deflector adapted to produce a force on the emitted ink droplets,
wherein the force is applied to the emitted ink droplets at an
angle with respect to the stream of ink droplets to cause the
emitted ink droplets having the first range of volumes to move
along a first path, and the emitted ink droplets having the second
range of volumes to move along a second path; d) a structure
integrated with the droplet deflector to provide a physically
separate gas flow for each of the stream of ink droplets; e) a
micro-controller adapted to adjust the emitted ink droplets having
the first and second range of volumes corresponding to either a
first or second operational state, respectively; and f) an ink
gutter positioned to allow the emitted ink droplets having the
first range of volumes moving along the first path to move
unobstructed past the ink gutter, while intercepting the emitted
ink droplets having the second range of volumes moving along the
second path.
13. The inkjet printhead claimed in claim 12, wherein the
physically separate gas flow for each of the stream of ink droplets
are operable due to thermal heating.
14. The inkjet printhead claimed in claim 12, wherein the
physically separate gas flow for each of the stream of ink droplets
are provided by individual jets as defined by a plurality of slits
in a plate structure such that a gas flow discriminator is
formed.
15. The inkjet printhead claimed in claim 12, wherein the
physically separate gas flow for each of the stream of ink droplets
are positive from a pressure source above ambient.
16. The inkjet printhead claimed in claim 12, wherein the
physically separate gas flow for each of the stream of ink droplets
are negative from a pressure source below ambient.
17. The inkjet printhead claimed in claim 12, wherein actuators are
provided in the droplet deflector, such that the physically
separate gas flow for each of the stream of ink droplets are
independently adjustable for each of the streams of ink
droplets.
18. The inkjet printhead claimed in claim 12, wherein the
physically separate gas flow for each of the stream of ink droplets
are applied in a direction substantially perpendicular to either or
both of the first or second paths.
19. The inkjet printhead claimed in claim 12, wherein either or
both of the first or second paths includes a gutter path.
20. The inkjet printhead claimed in claim 12, wherein either or
both of the first or second paths includes a printing path.
21. The inkjet printhead claimed in claim 14, wherein the plate
structure includes slits spaced equivalent to the one or more
nozzle bores.
22. The inkjet printhead claimed in claim 14, wherein the plate
structure includes a plenum that draws one of the first or second
volumes of streams of ink droplets into the plenum.
23. The inkjet printhead claimed in claim 17, wherein the actuators
respond to resistive heating from the passage of an electrical
current.
24. A method for selectively controlling ink droplets in an inkjet
printhead, comprising the steps of: a) emitting streams of ink
droplets having selectable first and second volumes; b) deflecting
the ink droplets having first and second volumes into first and
second paths, respectively; c) providing a plurality of separate
streams of gas; d) directing each of the plurality of separate
streams of gas at a corresponding one of the streams of ink
droplets to move the streams of ink droplets along the first and
second paths; and e) catching the ink droplets moving along one of
the first or second paths in an ink gutter.
25. The method claimed in claim 24, further comprising the steps
of: f) independently adjusting the plurality of separate streams of
gas according to each of the streams of ink droplets; and g)
directing the plurality of separate streams of gas substantially
perpendicular to one of the first or second paths.
26. The method claimed in claim 24, wherein one of the first or
second paths includes a gutter path.
27. The method claimed in claim 24, wherein one of the first or
second paths includes a printing path.
28. The method claimed in claim 24, wherein the plurality of
separate streams of gas are positive from a pressure source above
ambient.
29. The method claimed in claim 24, wherein the plurality of
separate streams of gas are negative from a pressure source below
ambient.
Description
FIELD OF THE INVENTION
This invention relates generally to the field of digitally
controlled printing devices, and in particular to continuous inkjet
printers wherein a liquid ink stream breaks into droplets, some of
which are selectively deflected.
BACKGROUND OF THE INVENTION
Continuous inkjet printing, uses a pressurized ink source that
produces a continuous stream of ink droplets. Conventional
continuous inkjet printers utilize electrostatic charging devices
that are placed close to the point where a filament of ink breaks
into individual ink droplets. The ink droplets are electrically
charged and then directed to an appropriate location by deflection
electrodes. When no printing is desired, the ink droplets are
directed into an ink-capturing mechanism (often referred to as a
catcher, interceptor, or gutter). When printing is desired, the ink
droplets are directed to strike a print media.
Typically, continuous inkjet printing devices are faster than
drop-on-demand devices and produce higher quality printed images
and graphics. However, each color printed requires an individual
droplet formation, deflection, and capturing system.
U.S. Pat. No. 1,941,001, issued to Hansell on Dec. 26, 1933, and
U.S. Pat. No. 3,373,437 issued to Sweet et al. on Mar. 12, 1968,
each disclose an array of continuous inkjet nozzles wherein ink
droplets to be printed are selectively charged and deflected
towards the recording medium. This technique is known as binary
deflection continuous inkjet.
U.S. Pat. No. 3,416,153, issued to Hertz et al. on Dec. 10, 1968,
discloses a method of achieving variable optical density of printed
spots in continuous inkjet printing using the electrostatic
dispersion of a charged droplet stream to modulate the number of
droplets which pass through a small aperture.
U.S. Pat. No. 3,878,519, issued to Eaton on Apr. 15, 1975,
discloses a method and apparatus for synchronizing droplet
formation in a liquid stream using electrostatic deflection by a
charging tunnel and deflection plates.
U.S. Pat. No. 4,346,387, issued to Hertz on Aug. 24, 1982,
discloses a method and apparatus for controlling the electric
charge on droplets formed by the breaking up of a pressurized
liquid stream at a droplet formation point located within the
electric field having an electric potential gradient. Droplet
formation is effected at a point in the field corresponding to the
desired predetermined charge to be placed on the droplets at the
point of their formation. In addition to charging tunnels,
deflection plates are used to actually deflect droplets.
U.S. Pat. No. 4,638,328, issued to Drake et al. on Jan. 20, 1987,
discloses a continuous inkjet printhead that utilizes constant
thermal pulses to agitate ink streams admitted through a plurality
of nozzles in order to break up the ink streams into droplets at a
fixed distance from the nozzles. At this point, the droplets are
individually charged by a charging electrode, and subsequently
deflected using deflection plates positioned in the droplet
path.
As conventional continuous inkjet printers utilize electrostatic
charging devices and deflector plates, they require many components
and large spatial volumes to operate. This results in continuous
inkjet printheads and printers that are complicated, have high
energy requirements, are difficult to manufacture, and are
difficult to control.
U.S. Pat. No. 3,709,432, issued to Robertson on Jan. 9, 1973,
discloses a method and apparatus for stimulating a filament of
working fluid causing the working fluid to break up into uniform
spaced ink droplets through the use of transducers. The lengths of
the filaments, before they break up into ink droplets, are
regulated by controlling the stimulation energy supplied to the
transducers. High amplitude stimulation causes short filaments and
low amplitude stimulations causes longer filaments. A flow of air
is generated across the paths of the fluid at a point intermediate
to the ends of the long and short filaments. The air flow affects
the trajectories of the filaments before they break up into
droplets, more than it affects the trajectories of the ink droplets
themselves. By controlling the lengths of the filaments, the
trajectories of the ink droplets can be controlled, or switched
from one path to another. As such, some ink droplets may be
directed into a catcher while allowing other ink droplets to be
applied to a receiving member.
While this method does not rely on electrostatic means to affect
the trajectory of droplets, it does rely on the precise control of
the break up points of the filaments and the placement of the air
flow intermediate to these break up points. Such a system is
difficult to control and to manufacture. Furthermore, the physical
separation or amount of discrimination between the two droplet
paths is small, further adding to the difficulty of control and
manufacture.
U.S. Pat. No. 4,190,844, issued to Taylor on Feb. 26, 1980,
discloses a continuous inkjet printer having a first pneumatic
deflector for deflecting non-printed ink droplets to a catcher and
a second pneumatic deflector for oscillating printed ink droplets.
A printhead supplies a filament of working fluid that breaks into
individual ink droplets. The ink droplets are then selectively
deflected by a first pneumatic deflector, a second pneumatic
deflector, or both. The first pneumatic deflector is an "ON/OFF"
type having a diaphragm that either opens or closes a nozzle
depending on one of two distinct electrical signals received from a
central control unit. This determines whether the ink droplet is
printed or not printed. The second pneumatic deflector is a
continuous type having a diaphragm that varies the amount that a
nozzle is open, depending on a varying electrical signal received
by the central control unit. This second pneumatic deflector
oscillates printed ink droplets so that characters may be printed
one character at a time. If only the first pneumatic deflector is
used, characters are created one line at a time, as a result of
repeated traverses of the printhead and ink build up.
While this method does not rely on electrostatic means to affect
the trajectory of droplets, it does rely on the precise control and
timing of the first ("ON/OFF") pneumatic deflector to create
printed and non-printed ink droplets. Such a system is difficult to
manufacture and accurately control, resulting in at least a similar
ink droplet build up as discussed above. Furthermore, the physical
separation or amount of discrimination between the two droplet
paths is erratic, due to the precise timing requirements,
therefore, increasing the difficulty of controlling printed and
non-printed ink droplets and resulting in poor ink droplet
trajectory control.
Additionally, using two pneumatic deflectors complicates
construction of the printhead and requires more components. The
additional components and complicated structure require large
spatial volumes between the printhead and the media, thereby,
increasing the ink droplet trajectory distance. Increasing the
distance of the droplet trajectory decreases droplet placement
accuracy and affects the print image quality. Again, there is a
need to minimize the distance that the droplet must travel before
striking the print media in order to insure high quality
images.
U.S. Pat. No. 6,079,821, issued to Chwalek et al. on Jun. 27, 2000,
discloses a continuous inkjet printer that uses actuation of
asymmetric heaters to create individual ink droplets from a
filament of working fluid and to deflect those ink droplets. A
printhead includes a pressurized ink source and an asymmetric
heater operable to form printed ink droplets and non-printed ink
droplets. Printed ink droplets flow along a printed ink droplet
path ultimately striking a receiving medium, while non-printed ink
droplets flow along a non-printed ink droplet path ultimately
striking a catcher surface. Non-printed ink droplets are recycled
or disposed of through an ink removal channel formed in the
catcher. While the inkjet printer disclosed in Chwalek et al. works
extremely well for its intended purpose, it is best adapted for use
with inks that have a large viscosity change with temperature.
Each of the above-described inkjet printing systems has advantages
and disadvantages. However, printheads which are low-power and
low-voltage in operation will be advantaged in the marketplace,
especially in page-width arrays. U.S. patent application Ser. No.
09/750,946, filed Dec. 28, 2000 by D. L. Jeanmaire et al. and U.S.
patent application Ser. No. 09/751,232, filed Dec. 28, 2000 by D.
L. Jeanmaire et al., disclose continuous inkjet printing wherein
nozzle heaters are selectively actuated at a plurality of
frequencies to create the stream of ink droplets having the
plurality of volumes. A gas stream provides a force separating
droplets into printing and non-printing paths according to droplet
volume. While this process consumes little power, and is suitable
for printing with a wide range of inks, when implemented in a
page-width array, a correspondingly wide laminar gas flow is
required. The wide laminar gas flow is often difficult to obtain
due to the mechanical tolerances involved in the gas flow plenum,
with the result that the gas velocity varies somewhat across the
printhead, and turbulent flow regions may exist. Non-uniform gas
flow has an adverse effect upon droplet placement on the print
medium, and therefore image quality is compromised.
It can be seen that there is a need to improve gas-flow uniformity
in the design of large nozzle-count printheads such as those used
in inkjet printers having page-width arrays.
SUMMARY OF THE INVENTION
The above need is met according to the present invention by
providing an inkjet printhead, that includes a plurality of nozzle
bores from which streams of ink droplets having selectable first
and second volumes are emitted; a droplet deflector for deflecting
the ink droplets having first and second volumes into first and
second paths respectively, the droplet deflector producing a
corresponding plurality of physically separate streams of gas, each
stream of gas directed on a corresponding one of the streams of ink
droplets; and an ink gutter positioned to catch the ink droplets
moving along one of the first or second paths.
Additionally, the present invention provides a method for
selectively controlling ink droplets in an inkjet printhead, which
includes the steps of: emitting streams of ink droplets having
selectable first and second volumes; deflecting the ink droplets
having first and second volumes into first and second paths,
respectively; providing a plurality of separate streams of gas;
directing each of the plurality of separate streams of gas at a
corresponding one of the streams of ink droplets to move the
streams of ink droplets along the first and second paths; and
catching the ink droplets moving along one of the first or second
paths in an ink gutter.
BRIEF DESCRIPTION OF THE DRAWINGS
Other features and advantages of the present invention will become
apparent from the following description of the preferred
embodiments of the invention, and the accompanying drawings,
wherein:
FIG. 1 is a prior art schematic diagram of a printing apparatus
incorporating a page-width printhead;
FIG. 2 is a top view of a printhead having a droplet forming
mechanism incorporating the present invention;
FIG. 3 is a schematic example of the electrical activation waveform
provided by the present invention;
FIG. 4 is a schematic example of the operation of an inkjet
printhead according to the present invention;
FIG. 5 is an isometric view of a gas discriminator according to the
present invention;
FIG. 6 is a schematic view showing droplet streams ejected from a
printhead incorporating the present invention;
FIGS. 7a-7f are schematic representations of the electrical
waveform of a heater in the present invention;
FIG. 8 is an isometric view of an aperture plate according to the
present invention;
FIG. 9 is a cross-sectional view of the aperture plate in FIG.
8;
FIG. 10 is an isometric view of the printhead assembly as droplet
streams are emitted according to the present invention;
FIG. 11 shows an alternate embodiment of the present invention;
and
FIG. 12 shows still another embodiment of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be directed in particular to elements
forming part of, or cooperating more directly with the present
invention. It is to be understood that elements not specifically
shown or described may take various forms that are well known to
those skilled in the art.
Referring to FIG. 1, a prior art continuous inkjet printer system 5
is shown. The continuous inkjet printer system 5 includes an image
source 10 such as a scanner or computer which provides raster image
data, outline image data in the form of a page description
language, or other forms of digital image data. This digital image
data is converted to half-toned bitmap image data by an image
processing unit 12, which also stores the digital image data in
image memory 13. A heater control circuit 14 reads data from the
image memory 13 and applies electrical pulses to a heater 32 that
is part of a printhead 16. These pulses are applied at an
appropriate time, so that droplets formed from a continuous inkjet
stream will print spots on a recording medium 18, in the
appropriate position, designated by the data in the image memory
13. The printhead 16, shown in FIG. 1, is commonly referred to as a
page-width printhead.
Recording medium 18 is moved relative to printhead 16 by a
recording medium transport system 20 which is electronically
controlled by a recording medium transport control system 22, and
which in turn is controlled by a micro-controller 24. The recording
medium transport system 20 shown in FIG. 1 is a schematic only, and
many different mechanical configurations are possible. For example,
a transfer roller could be used as recording medium transport
system 20 to facilitate transfer of the ink droplets to recording
medium 18. Such transfer roller technology is well known in the
art. In the case of page-width printheads 16, it is most convenient
to move recording medium 18 past a stationary printhead 16.
Ink is contained in an ink reservoir 28 under pressure. In the
nonprinting state, continuous inkjet droplet streams are unable to
reach recording medium 18 due to an ink gutter 34 that blocks the
stream and which may allow a portion of the ink to be recycled by
an ink recycling unit 36. The ink recycling unit 36 reconditions
the ink and feeds it back to ink reservoir 28. Such ink recycling
units 36 are well known in the art. The ink pressure suitable for
optimal operation will depend on a number of factors, including
geometry and thermal properties of the nozzle bores 42 (shown in
FIG. 2) and thermal properties of the ink. A constant ink pressure
can be achieved by applying pressure to ink reservoir 28 under the
control of ink pressure regulator 26.
Continuous inkjet printers system 5 can incorporate additional ink
reservoirs 28 in order to facilitate color printing. When operated
in this fashion, ink collected by ink gutter 34 is typically
collected and disposed.
The ink is distributed to the back surface of printhead 16 by an
ink channel 30. The ink, preferably, flows through slots and/or
holes etched through a silicon substrate of printhead 16 to its
front surface where a plurality of nozzles and heaters are
situated. With printhead 16 fabricated from silicon, it is possible
to integrate heater control circuits 14 with the printhead 16.
Printhead 16 can be formed using known semiconductor fabrication
techniques (including CMOS circuit fabrication techniques,
micro-electro mechanical structure MEMS fabrication techniques,
etc.). Printhead 16 can also be formed from semiconductor materials
other than silicon, for example, glass, ceramic, or plastic.
Referring to FIG. 2, printhead 16 is shown in more detail.
Printhead 16 includes a droplet forming mechanism 38. Droplet
forming mechanism 38 can include a plurality of heaters 40
positioned on printhead 16 around a plurality of nozzle bores 42
formed in printhead 16. Although each heater 40 may be radially
disposed away from an edge of a corresponding nozzle bore 42,
heaters 40 are, preferably, disposed close to corresponding nozzle
bores 42 in a concentric manner. Typically, heaters 40 are formed
in a substantially circular or ring shape. However, heaters 40 can
be formed in other shapes. Conventionally, each heater 40 has a
resistive heating element 44 electrically connected to a contact
pad 46 via a conductor 48. A passivation layer (not shown), formed
from silicon nitride is normally placed over the resistive heating
elements 44 and conductors 48 to provide electrical insulation
relative to the ink. Contact pads 46 and conductors 48 form a
portion of the heater control circuits 14 which are connected to
micro-controller 24. Alternatively, other types of heaters can be
used with similar results.
Heaters 40 are selectively actuated to from droplets. The volume of
the formed droplets is a function of the rate of ink flow through
the nozzle bore 42 and the rate of heater activation, but is
independent of the amount of energy dissipated in the heaters. FIG.
3 is a schematic example of the electrical activation waveform
provided by micro-controller 24 to heaters 40. In general, rapid
pulsing of heaters 40 forms small ink droplets, while slower
pulsing creates larger droplets. In the example presented herein,
small ink droplets are to be used for marking the recording medium
18, while larger, non-printable droplets are captured for ink
recycling.
Consequently, multiple droplets per nozzle per image pixel are
created. Periods P.sub.0, P.sub.1, P.sub.2, etc. are the times
associated with the printing of associated image pixels, the
subscripts indicate the number of printing droplets created during
the pixel time. The schematic illustration shows the droplets that
are created as a result of the application of the various
waveforms. A maximum of two small printing droplets is shown for
simplicity of illustration, however, the concept can be readily
extended to permit a higher maximum count of printing droplets.
In the droplet formation for each image pixel, a non-printable
large droplet 95, 105, or 110 is always created, in addition to a
select number of small, printable droplets 100. The waveform of
activation for heater 40, for every image pixel, begins with an
electrical pulse time 65. The further (optional) activation of
heater 40, after delay time 83, with an electrical pulse 70, is
conducted in accordance with image data, wherein at least one
printable droplet 100 is required as shown for interval P.sub.1.
For cases where the image data requires that still another
printable droplet 100 be created as in interval P.sub.2, heater 40
is again activated, after delay 84, with a pulse 75. Heater
activation. electrical pulse times 65, 70, and 75 are substantially
similar, as are all delay times 83 and 84. Delay times 80, 85, and
90 are the remaining times after pulsing is over in a pixel time
interval P, and the start of the next image pixel. All small
printable droplets 100 are the same volume. However, the volume of
the larger, non-printable droplets 95, 105 and 110 varies depending
on the number of small printable droplets 100 created in the
preceding pixel time interval P as the creation of small droplets
takes mass away from large droplets during the pixel time interval
P. The delay time 90 is preferably chosen to be significantly
larger than the delay times 83, 84, so that the volume ratio of
large non-printable-droplets 110 to small printable droplets 100 is
a factor of 4 or greater.
FIG. 4 is a schematic example of the operation of printhead 16 in a
manner that provides one printing droplet per pixel. Printhead 16
is coupled with a gas-flow discriminator 130 which separates
droplets into printing or non-printing paths, according to droplet
volume. Ink is ejected through nozzle bores 42 in printhead 16,
thus creating a filament of working fluid 62 that moves
substantially perpendicular to printhead 16 along axis X. Heaters
40 are selectively activated at various frequencies according to
image data, causing filaments of working fluid 62 to break up into
streams of individual ink droplets. Coalescencing of droplets often
occurs when forming non-printable droplets 105. The gas flow
discriminator 130 is provided by a gas flowing at a non-zero angle
with respect to axis X. As one example, the gas flow may be
perpendicular to axis X. Gas flow discriminator 130 acts over
distance L, and as a gaseous force from gas flow discriminator 130
interacts with the stream of ink droplets, the individual ink
droplets separate, depending on individual volume and mass. The gas
flow rate can be adjusted to provide sufficient deviation D between
the small droplet path S and the large droplet paths K, thereby
permitting small printable droplets 100 to strike print media W,
while large non-printable droplets 105 are captured by an ink
guttering structure 240.
In one embodiment of the present invention, a gas flow
discriminator 130 is shaped by a plenum (not shown) fitted with an
exit aperture plate 200 or cap as shown in FIG. 5. This plate is a
structure with holes or slits 210 that serve to channel gas flow
into individual jets, where the pitch of the openings is
essentially the same as the nozzle pitch on the printhead. In this
manner, each ink droplet stream has an associated gas flow stream.
Exit aperture plate 200 is formed from silicon, using known
semiconductor fabrication techniques (such as, micro-electro
mechanical structure (MEMS) fabrication techniques, etc.). However,
exit aperture plate 200 may be formed from any materials (e.g.
plastics, ceramics, metal, etc.) using any fabrication techniques
conventionally known in the art. Due to the fact that the total
area of exit slits 210 is less than the cross-sectional area of the
plenum, a pressure droplet is created across the exit aperture
plate 200. This serves to increase the uniformity in the velocity
of gas flow across the exit aperture plate 200 from slit-to-slit,
as well as reduce gas-flow turbulence.
Referring now to FIG. 6, which is a schematic view incorporating an
embodiment of the current invention, droplet streams are ejected
from printhead 16. As discussed earlier with reference to FIG. 3,
but not shown herein, droplet forming mechanism 38 is actuated such
that droplets of ink having a plurality of volumes 95, 100, 105 and
110 (as shown in FIG. 3) traveling along paths X (FIG. 6) are
formed. A gas flow discriminator 130 supplied from a droplet
deflector system 56, including a gas flow source 58 (not shown),
plenum 220, and exit aperture plate 200, is continuously applied to
droplets 95, 100, 105 and 110 over an interaction distance L.
Because droplets 95, 105 and 110 have a larger volume (in addition
to more momentum and greater mass) than droplets 100, droplets 100
deviate from path X and begin traveling along path S; while
droplets 95, 105 and 110 remain traveling, substantially, along
path X or deviate slightly from path X and begin traveling along
path K. With appropriate adjustment of gas flow discriminator 130,
and appropriate positioning of the ink guttering structure 240,
droplets 100 contact print media W at location 250, while droplets
95, 105 and 110 are collected by ink guttering structure 240.
In another embodiment of the current invention, the principle of
the printing operation is reversed, where the larger droplets are
used for printing, and the smaller droplets recycled. An example of
this mode is presented here. In this example, only one printing
droplet is provided for per image pixel, thus there are two states
of heater 40 actuation, printing or non-printing. The electrical
waveform of heater 40 actuation for the printing case is presented
schematically as FIG. 7a. The individual large non-printable
droplets 95 resulting from the jetting of ink from nozzle bores 42,
in combination with this electrical pulse time 65 and delay times
80, are shown schematically as FIG. 7b. The electrical waveform of
heater 40 activation for the non-printing case is given
schematically as FIG. 7c. Electrical pulse time 65 duration remains
unchanged from FIG. 7a, however, time delay 83 between activation
pulses is a factor of 4 and shorter than delay time 80. The small
droplets 100, as diagrammed in FIG. 7d, are the result of the
activation of heater 40 with this non-printing waveform.
FIG. 7e is a schematic representation of the electrical waveform of
heater 40's activation for mixed image data. A transition from the
non-printing state to the printing state, and back again to the
non-printing state is shown. A schematic representation is shown of
the resultant formed droplet stream, FIG. 7f. Heater 40's
activation may be independently controlled, based on a required ink
color, and ejecting the desired ink through corresponding nozzle
bores 42; or moving printhead 16 relative to a print media W. In
one embodiment of this invention, the function of droplet
deflection is combined physically with that of ink guttering. This
combined assembly allows for a more compact physical
implementation, and thus the printhead 16 can be closer to the
print media W for improved droplet placement. Referring to FIG. 8,
in this configuration, vacuum aperture plate 260 consists of holes
or slots 270 to permit the entry of gas into a plenum (not shown).
The air pressure in the plenum is below ambient, such that air
flows from the external environment into vacuum aperture plate 260.
Slots 270 are spaced at the same pitch as the nozzles on printhead
16. Vacuum aperture plate 260 also contains guttering ribs 280 and
relief channel 290 whose functions will become more clear from the
following discussion.
FIG. 9 is an end-on cross-sectional view of vacuum aperture plate
260 taken through the center of a slot 270. As an example here,
vacuum aperture plate 260 is fabricated from silicon, and was
constructed by bonding wafers 300 and 310 together, after etching
steps were completed. Vacuum aperture plate 260 is then adhesively
joined to the end of plenum 220. Droplet streams ejected from
printhead 16 consisting of large non-printable droplets 95 and
small printable droplets 100 initially pass over droplet deflection
system 56 and interact with gas flow discriminator 130. Small
printable droplets 100 are deflected into slot 270 and strike
guttering rib 280 before being drawn down into plenum 220.
Guttering rib 280 has a top plate which overhangs slot 270 to
prevent ink from splattering over guttering rib 280 and down the
outside of droplet deflection system 56. Large non-printable
droplets 95 pass over guttering rib 280 and are allowed to strike
print media W. Relief channel 290 provides clearance for large
non-printable droplets 95, so that they do not strike the top of
vacuum aperture plate 260.
An overall view of a printhead assembly using this embodiment is
given in FIG. 10. As droplet streams are emitted from printhead 16,
they pass over droplet deflector system 56. Small ink droplets 100
are deflected from initial path X, and are drawn into plenum 220.
Large droplets 95 are only slightly deflected onto path K which
clears the guttering elements of vacuum aperture plate 260, and the
droplets then strike print media W at locations 250.
An alternate embodiment of this invention for the design of a
droplet deflector 430 involves the formation of gas-flow channels
410 in a substrate 400 as shown in FIG. 11. The substrate 400 may
be ceramic, metal, plastic, etc. however, silicon is preferred. A
cover plate 420 is adhesively bonded to substrate 400, thereby
forming one side of the gas-flow channels 410. As in the previous
embodiment, there is a one-to-one correspondence between gas-flow
channels 410 and individual jets (not shown) on the printhead 16. A
manifold (not shown) couples a gas source (or vacuum) into the
gas-flow channels 410. An advantage of this embodiment is that the
droplet deflector system 56 is a more mechanically durable
structure, however, the structure is more expensive due to
increased silicon consumption.
A modification of droplet deflector 430 is envisioned wherein cover
plate 420 is manufactured with plural thermal-bend-actuators 440
disposed on the surface as shown in FIG. 12. The
thermal-bend-actuators may be formed from a bi-layer of TiAl and
SiN, for example. They are positioned such that when cover plate
420 is bonded to substrate 400, there is a thermal-bend-actuator in
each of the gas-flow channels 410. In the rest or non-activated
state, the thermal-bend-actuators lie flat against cover plate 420,
and thus do not impede gas flow in gas -flow channels 410. When the
thermal-bend-actuators 440 experience resistive heating due to the
passage of electrical current as directed by micro-controller 24,
they bend away from cover plate 420 and restrict gas flow.
Generally, larger electrical currents produce larger actuator
bending, so that the gas flow may be individually regulated in each
gas-flow channel 410. This control of gas flow allows the
deflection of each individual jet on the printhead to be balanced
for optimum operation.
While the foregoing description includes many details and
specificities, it is to be understood that these have been included
for purposes of explanation only, and are not to be interpreted as
limitations of the present invention. Many modifications to the
embodiments described above can be made without departing from the
spirit and scope of the invention, as is intended to be encompassed
by the following claims and their legal equivalents.
PARTS LIST 5 continuous inkjet printer system 10 image source 12
image processing unit 13 image memory 14 heater control circuit 16
printhead 18 recording medium 20 recording medium transport system
22 recording medium transport control system 24 micro-controller 26
ink pressure regulator 28 ink reservoir 30 ink channel 32 heater 34
ink gutter 36 ink recycling unit 38 droplet forming mechanism 40
heater 42 nozzle bore 44 resistive heating element 46 contact pad
48 conductor 56 droplet deflector system 58 gas flow source 62
filament of working fluid 65 electrical pulse time 70 electrical
pulse time 75 electrical pulse time 80 delay time 83 delay time 84
delay time 85 delay time 90 delay time 95 large non-printable
droplets 100 small printable droplets 105 large non-printable
droplets 110 large non-printable droplets 130 gas flow
discriminator 200 exit aperture plate 210 exit slits 220 plenum 240
ink guttering structure 250 location of print media 260 vacuum
aperture plate 270 slots 280 guttering ribs 290 relief channel 300
bonding wafer 310 bonding wafer 400 substrate 410 gas-flow channels
420 cover plate 430 droplet deflector 440
thermal-bend-actuators
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